Space Charge Measurement Method for Model HVDC Cable at High Conductor Temperature

Polymer insulated HVDC power cable is being implemented for submarine transmission. Since the insulation is exposed to a high temperature originating from the current in the conductor, space charge can be easily injected to the insulation which generates a distortion of electrical field. The space charge measurement for HVDC cable by Pulse Electro-Acoustic (PEA) technique. In this study, we proposed a method to estimate the conductor temperature at high temperature for the result of the charge distribution. Space charge measurement was applied for a model cable with the construction of 3 mm polymer insulation thickness, 1.025 mm for outer semiconductor, 1.05 mm for inner semiconductors and conductor diameter 14.35 mm. A high current at the conductor was generated by adjusting the current flowing through the Current Transformer (CT) and it heated up the cable. Then, space charge was measured by using a PEA technique. Space charge distribution was investigated by applying the 30 kV DC at room or high conductor temperature. By the detection time difference between the signal of the conductor and ground electrode, sound speed for XLPE at room temperature was different from XLPE at high temperature. Supposing that the change of the detection time difference lead by changing the sound speed of XLPE at high conductor temperature. It was suggested that the conductor temperature can be predicted by space charge measurement without directly measuring the conductor temperature. Space charge is significantly accumulated at high conductor temperature and its phenomena can be investigated by using the developed equipment.